1. Field of the Invention
The invention relates to a novel method, system, sensor and sensor/guide wire assembly for measuring physiological variables inside the body of a human or an animal. More particularly, it relates to a wireless sensor having a diaphragm comprising elements responsive to resonance.
2. Description of Related Art
Intravascular measurements of pressure, flow, and temperature via sensors mounted to guidewires, as disclosed in U.S. Pat. No. 5,226,423, Tenerz, reissued as Re. 35,648, are of particular interest to the health care industry, and serve as tangible examples of embodiments of system solutions, device designs, components and materials to be used in the realization of the invention.
Implantable devices for physiological measurements and therapy have been used for decades, for example, in combination with cardiac pacemakers. These device carry their own power supply, are relatively bulky, and require a surgical procedure to be implanted into the patient""s body.
For short term diagnostic procedures, such as intravascular measurements of pressure, flow, and temperature, the current state of the art utilizes micromechanical sensor elements, mostly silicon devices based on well known piezoresistive, capacitive, or fiber optic principles. The devices communicate information and power along a guidewire via thin optical fibers or insulated electrical leads. The guidewire is extremely small, preferably with an overall diameter no larger than 0.4 mm. Housing multiple wires in a guide wire with such an extremely small area is very difficult from a technological standpoint and is also very costly. Other difficulties arise, including, maintaining the structural integrity and the mechanical properties of the guidewire while encompassing within the guide wire the power and information transmission media. Moreover, weak points, in terms of sensor performance (e.g., zero point stability) and mechanical reliability, exist at the connecting points between the sensor and the information and power transmission wires.
A wireless system for recording pressure in the eye is disclosed in the following articles: xe2x80x9cPassive Silicon Transensor Intended for Biomedical, Remote pressure Monitoringxe2x80x9d by Bxc3xa4cklund, Y. et al in Sensors and Actuators, A21-A23 (1990) 58-61, Elsevier Sequoia; xe2x80x9cA System for Wireless Intra-ocular Pressure Measurements Using Silicon Micromachined sensorxe2x80x9d by Rosengren, L. et al. in J. Of Micromech. Microeng. 2(1992) 202-204, IOP Publishing Ltd; and xe2x80x9cA system for Passive Pressure Implantable Pressure Sensorsxe2x80x9d by Rosengren, L. et al in Sensors and Actuators A, 1994, Elsevier Sequoia. The disclosures of these publications are hereby incorporated in this specification by reference.
The wireless system disclosed in these articles comprises an electromagnetic sensor device of an L-C circuit type, having the capability of resonating in response to an excitation by an externally applied electromagnetic field, and to change is resonance frequency in response to a pressure change. The sensor is implanted/inserted into the eye, and excitation energy is applied. The shift in resonance frequency due to change in pressure exerted on the device is registered.
The difficulties suggested in the preceding are not intended to be exhaustive but rather are among many which tend to reduce the desirability of the known devices. Other noteworthy problems may exist; however, those presented above should be sufficient to demonstrate that such methods and apparatuses appearing in the past will admit to worthwhile improvement.
Accordingly, it is therefore a general object of the invention to provide a method and apparatus that will obviate or minimize difficulties of the type previously described.
It is a specific object of the invention to provide a method and device for measuring physiological variables able to transmit information without the use of wires.
It is another object of the invention to provide a device with high mechanical reliability for measuring physiological variables.
It is still another object to provide a relatively small device for measuring physiological variables.
It is a further object to provide a device for measuring physiological variables that has virtually no weak points.
It is yet a further object of the invention to provide a device that can be produced in a cost effective manner.
It is still a further object of the invention to provide a method for measuring physiological variables inside a human or an animal body.
For the purpose of this application, a xe2x80x9cresonance sensorxe2x80x9d is meant to encompass any device that has the capability of resonating at a defined frequency upon excitation by energy/power from an external source, i.e. without physical contact between source and device, and in addition to have the capability of changing its resonance frequency in a defined way as a result of a change of a physical variable, such as pressure, temperature or fluid flow, that the device is being exposed to. Alternatively, the quality factor of the resonating device may be affected by said change, and can be used for detection purposes.
A preferred embodiment of the invention that is intended to accomplish at least some of the foregoing objects includes a guidewire and a sensor element attached to said guidewire, wherein said sensor element has no wires for transmitting or receiving information. A preferred method includes inserting a guidewire into a patient""s body; transmitting waves to a sensor mounted on the guidewire; redistributing the waves, the redistributing being a function of the physiological variable; and receiving the redistributed waves.
Additional objects and advantages of the invention will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims.